Methods for detecting atrial tachyarrhythmia in implantable devices without dedicated atrial sensing

ABSTRACT

An apparatus comprises an implantable cardiac signal sensing circuit configured to provide a sensed depolarization signal from a ventricle and a processor. The processor includes a signal analyzer module and a tachyarrhythmia discrimination module. The signal analyzer module is configured to determine a measure of stability of ventricular (V−V) depolarization intervals using the depolarization signal, and determine a rate of change of the measure of stability. The tachyarrhythmia discrimination module is configured to detect an episode of tachyarrhythmia using the depolarization signal, determine whether the detected tachyarrhythmia is indicative of atrial tachyarrhythmia using the determined rate of change, and provide the determination to a user or process.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 12/754,932,filed Apr. 6, 2010, which claims the benefit of U.S. ProvisionalApplication No. 61/171,739, filed on Apr. 22, 2009, under 35 U.S.C.§119(e), which is hereby incorporated by reference.

BACKGROUND

Implantable medical devices (IMDs) include devices designed to beimplanted into a patient. Some examples of these devices include cardiacfunction management (CFM) devices such as implantable pacemakers,implantable cardioverter defibrillators (ICDs), cardiacresynchronization therapy devices (CRTs), and devices that include acombination of such capabilities. The devices can be used to treatpatients using electrical or other therapy or to aid a physician orcaregiver in patient diagnosis through internal monitoring of apatient's condition. The devices may include one or more electrodes incommunication with one or more sense amplifiers to monitor electricalheart activity within a patient, and often include one or more sensorsto monitor one or more other internal patient parameters. Other examplesof implantable medical devices include implantable diagnostic devices,implantable drug delivery systems, or implantable devices with neuralstimulation capability.

Additionally, some IMDs detect events by monitoring electrical heartactivity signals. In CFM devices, these events can include heart chamberexpansions or contractions. By monitoring cardiac signals indicative ofexpansions or contractions, IMDs can detect abnormally slow heart rate,or bradycardia. Some IMDs detect abnormally rapid heart rate, ortachyarrhythmia. Tachyarrhythmia includes ventricular tachycardia (VT)and supraventricular tachycardia (SVT). Tachyarrhythmia also includesrapid and irregular heart rate, or fibrillation, including ventricularfibrillation (VF).

When detected, ventricular tachyarrhythmia can be terminated withhigh-energy shock therapy delivered with an ICD.Cardioversion/defibrillation therapy can cause patient discomfort andconsumes a relatively large amount of battery power which may lead to ashortened useful device lifetime. Some ICDs are single chamber devicesthat sense cardiac signals and deliver therapy to a single heart chamber(e.g., the right ventricle). However, ICD patients may develop atrialarrhythmias. Atrial tachyarrhythmia includes atrial fibrillation (AF)and atrial tachycardia (AT). Atrial tachyarrhythmia with a fastventricular response (e.g., resulting in a fast ventricular rate) isoften a cause of inappropriate shocks by an ICD.

Overview

This document relates generally to systems, devices, and methods formonitoring cardiac electrophysiological parameters of a patient orsubject. Episodes of atrial and ventricular tachyarrhythmia are alsomonitored.

In example 1, an apparatus includes an implantable cardiac signalsensing circuit configured to provide a sensed depolarization signalfrom a ventricle and a processor communicatively coupled to the cardiacsignal sensing circuit. The processor includes a signal analyzer moduleand a tachyarrhythmia discrimination module. The signal analyzer moduleis configured to determine a measure of stability of ventricular (V−V)depolarization intervals using the depolarization signal, and determinea rate of change of the measure of stability. The tachyarrhythmiadiscrimination module is configured to detect an episode oftachyarrhythmia using the depolarization signal, determine whether thedetected tachyarrhythmia is indicative of atrial tachyarrhythmia usingthe determined rate of change, and provide the determination to a useror process.

In example 2, the tachyarrhythmia discrimination module of example 1 isoptionally configured to classify the detected tachyarrhythmia as atrialtachyarrhythmia when the rate of change of the measure of stabilityexceeds an atrial tachyarrhythmia rate of change detection threshold.

In example 3, the tachyarrhythmia discrimination module of examples 1and 2 is optionally configured to classify the detected tachyarrhythmiaas ventricular tachyarrhythmia when the rate of change of the measure ofstability is greater than a ventricular tachyarrhythmia rate of changedetection threshold and is less than the atrial tachyarrhythmia rate ofchange detection threshold.

In example 4, the signal analyzer module of examples 1-3 is optionallyconfigured to determine a rate of change of the measure of stabilitywhen a ventricular depolarization rate or interval satisfies a specifiedthreshold rate or threshold interval value. The tachyarrhythmiadiscrimination module is optionally configured to classify the detectedtachyarrhythmia according to the rate of change of the measure ofstability when the ventricular rate or interval satisfies the specifiedthreshold value, and classify the detected tachyarrhythmia according tothe measure of stability otherwise.

In example 5, the apparatus of examples 1-4 optionally includes a memorycommunicatively coupled to the processor and configured to a store asignal morphology template, and a far-field sensing channel configuredto provide a far-field atrial and ventricular signal using an electrodelocation that is outside of an atrium or ventricle. The tachyarrhythmiadiscrimination module is optionally configured to, upon determining thedetected tachyarrhythmia is atrial tachyarrhythmia, initiate sensing ofthe far-field signal, initiate a comparison of a morphology of thesensed far-field signal to a stored morphology template by the signalanalyzer module, and confirm the classification as atrialtachyarrhythmia using the morphology comparison.

In example 6, the signal analyzer module of example 5 is optionallyconfigured to calculate a measure of similarity between a segment of thefar-field signal and the morphology template which is representative ofnormal sinus rhythm, and calculate a central tendency of the measure ofsimilarity and a variance of the measure of similarity. Thetachyarrhythmia discrimination module is optionally configured toconfirm the classification as atrial tachyarrhythmia when the centraltendency of the measure of similarity is above a central tendencythreshold and the variance of the measure of similarity is within avariance range.

In example 7, the stored morphology template of examples 5 and 6 isoptionally associated with atrial tachyarrhythmia.

In example 8, apparatus of examples 1-7 optionally includes a memory anda communication circuit communicatively coupled to the processor. Thecommunication circuit is configured to communicate informationwirelessly with a second separate device. The tachyarrhythmiadiscrimination module is optionally configured to upon classifying thedetected tachyarrhythmia as atrial tachyarrhythmia, initiate storage ofa segment of the depolarization signal when a duration of the detectedtachyarrhythmia exceeds a duration threshold, initiate storage of ahistogram of V−V depolarization intervals, wherein the histogramindicates regular and irregular V−V depolarization intervals, andcommunicate the stored segment and histogram to a second device.

In example 9, the apparatus of examples 1-4 optionally includes afar-field sensing channel configured to provide a far-field atrialsignal using an electrode location that is outside of an atrium, amemory communicatively coupled to the processor, and a communicationcircuit, communicatively coupled to the processor, configured tocommunicate information wirelessly with a second separate device. Thetachyarrhythmia discrimination module is optionally configured to uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,initiate storage of a segment of the sensed far-field signal when aduration of the detected arrhythmia exceeds a duration threshold,communicate the stored segment to the second device for comparison of afar-field signal morphology to a morphology template, and receive anindication whether the detected tachyarrhythmia is atrialtachyarrhythmia from the second device.

In example 10, a method includes detecting an episode of tachyarrhythmiafrom a depolarization signal sensed from a ventricle using a dedicatedimplantable ventricular sensing circuit and in an absence of a dedicatedatrial chamber sensing circuit, determining a measure of stability ofV−V depolarization intervals using the depolarization signal,determining a rate of change of the measure of stability, classifyingthe detected tachyarrhythmia as atrial tachyarrhythmia or ventriculartachyarrhythmia using the determined rate of change, and providing thetachyarrhythmia classification to a user or process.

In example 11, the classifying the detected tachyarrhythmia of example10 optionally includes classifying the detected tachyarrhythmia asatrial tachyarrhythmia when the rate of change of the measure ofstability exceeds an atrial tachyarrhythmia rate of change detectionthreshold.

In example 12, the classifying the detected tachyarrhythmia of examples10 and 11 optionally includes classifying the detected tachyarrhythmiaas ventricular tachyarrhythmia when the rate of change of the measure ofstability is greater than a ventricular tachyarrhythmia rate of changedetection threshold and is less than the atrial tachyarrhythmia rate ofchange detection threshold.

In example 13, the determining a rate of change of the measure ofstability of examples 10-12 optionally includes determining a rate ofchange of the measure of stability when the ventricular rate or intervalsatisfies a threshold rate or interval value. The classifying thedetected tachyarrhythmia optionally includes classifying the detectedtachyarrhythmia according to the rate of change of the measure ofstability when the ventricular rate or interval satisfies the thresholdrate or interval value, and classifying the detected tachyarrhythmiaaccording to the measure of stability otherwise.

In example 14, the method of examples 10-13 optionally includes, uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,sensing a second signal using a far-field sensing channel and comparinga morphology of the second sensed signal to a morphology template. Theclassifying the tachyarrhythmia optionally includes confirming theclassification as atrial tachyarrhythmia using the morphologycomparison.

In example 15, the classifying the tachyarrhythmia of example 14optionally includes calculating a measure of similarity between asegment of the second signal and the morphology template, wherein themorphology template is representative of normal sinus rhythm,calculating a central tendency of the measure of similarity and avariance of the measure of similarity. The confirming the classificationoptionally includes confirming the classification as atrialtachyarrhythmia when the central tendency of the measure of similarityis above a central tendency threshold and the variance of the measure ofsimilarity is within a variance range.

In example 16, the classifying the tachyarrhythmia of example 14optionally includes, upon classifying the detected tachyarrhythmia asatrial tachyarrhythmia, storing a segment of the second signal when aduration of the detected arrhythmia exceeds a duration threshold. Thecomparing a morphology optionally includes communicating the storedsegment from a first implantable medical device to a second device andcomparing the morphology of the second sensed signal to the morphologytemplate using the second device, and the classification optionallyincludes confirming the classification as atrial tachyarrhythmia usingthe morphology comparison by the second device.

In example 17, the comparing a morphology of the second signal ofexamples 14-16 optionally includes comparing a morphology of the secondsensed signal to a morphology template associated with atrialtachyarrhythmia.

In example 18, the method of examples 10-17 optionally includes, uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,storing a segment of the depolarization signal when a duration of thedetected tachyarrhythmia exceeds a duration threshold, storing ahistogram of V−V depolarization intervals, wherein the histogramindicates regular and irregular V−V depolarization intervals, andcommunicating the stored segment and histogram from an implantablemedical device to a second device.

In example 19, an apparatus includes an implantable cardiac signalsensing circuit, configured to provide a sensed depolarization signalfrom a ventricle, and a processor. The processor is communicativelycoupled to the cardiac signal sensing circuit and includes a signalanalyzer module configured to measure V−V depolarization intervals and atachyarrhythmia discrimination module configured to detect an episode oftachyarrhythmia using the measured V−V depolarization intervals, detecta sudden presence of long and short V−V depolarization intervals,classify the detected tachyarrhythmia as atrial tachyarrhythmia orventricular tachyarrhythmia using a detected pattern of long and shortV−V depolarization intervals, and provide the tachyarrhythmiaclassification to a user or process.

In example 20, the apparatus of example 19 optionally includes a memorycommunicatively coupled to the processor and configured to a store asignal morphology template and a far-field sensing channel configured toprovide a far-field atrial and ventricular signal using an electrodelocation that is outside of an atrium or ventricle. The tachyarrhythmiadiscrimination module is optionally configured to, upon classifying thedetected tachyarrhythmia as atrial tachyarrhythmia, initiate sensing ofthe far-field signal, and initiate a comparison a morphology of thefar-field signal to a stored morphology template by the signal analyzermodule, and confirm the classification as atrial tachyarrhythmia usingthe morphology comparison.

In example 21, the signal analyzer module of examples 19 and 20 isoptionally configured to calculate a measure of similarity between asegment of the far-field signal and the morphology template, wherein thestored morphology template is representative of normal sinus rhythm, andcalculate a central tendency of the measure of similarity and a varianceof the measure of similarity. The tachyarrhythmia discrimination moduleis optionally configured to confirm the classification as atrialtachyarrhythmia when the central tendency of the measure of similarityis above a central tendency threshold, the variance of the measure ofsimilarity is within a variance range, and the depolarization rate orinterval satisfies a rate or interval detection threshold.

In example 22, the apparatus of examples 19-21 optionally includes amemory and a communication circuit communicatively coupled to theprocessor. The communication circuit is configured to communicateinformation wirelessly with a second separate device. Thetachyarrhythmia discrimination module is optionally configured to, uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,initiate storage of a segment of the depolarization signal when aduration of the detected arrhythmia exceeds a duration threshold,initiate storage of a histogram of V−V depolarization intervals, whereinthe histogram indicates regular and irregular V−V depolarizationintervals, and communicate the stored segment and histogram from animplantable medical device to a second device.

In example 23, a method includes detecting an episode of tachyarrhythmiausing a depolarization signal sensed from a ventricle in an absence of adedicated atrial chamber sensing circuit, detecting a sudden presence oflong and short V−V depolarization intervals using the depolarizationsignal, classifying the detected tachyarrhythmia as atrialtachyarrhythmia or ventricular tachyarrhythmia using a detected patternof long and short V−V depolarization intervals, and providing thetachyarrhythmia classification to a user or process.

In example 24, the method of example 23 optionally includes, uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,sensing a second signal using a far-field sensing channel, and comparinga morphology of the second sensed signal to a morphology template. Theclassifying the tachyarrhythmia optionally includes confirming theclassification as atrial tachyarrhythmia using the morphologycomparison.

In example 25, the method of example 23 and 24 optionally includes, uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,storing a segment of the depolarization signal when a duration of thedetected arrhythmia exceeds a duration threshold, storing a histogram ofV−V depolarization intervals, wherein the histogram indicates regularand irregular V−V depolarization intervals, and communicating the storedsegment and histogram from an implantable medical device to a seconddevice.

This section is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is an illustration of an example of portions of a system thatincludes an IMD.

FIG. 2 is a flow diagram of an example of a method of detecting andclassifying atrial tachyarrhythmia using an IMD.

FIG. 3 is a block diagram of portions of an example of an IMD to detectand classify atrial tachyarrhythmia.

FIG. 4 is a flow diagram of an example of a method of detecting atrialtachyarrhythmia using an IMB that does not have dedicated atrial sensingcircuits.

FIG. 5 shows an example of a characteristic pattern of V−V intervalsduring an AF episode.

DETAILED DESCRIPTION

This document discusses systems and methods for improved detection ofcardiac events by an IMD. Specifically systems and methods for improveddiscrimination or classification of tachyarrhythmia by an IMB aredescribed.

An implantable medical device (IMD) may include one or more of thefeatures, structures, methods, or combinations thereof described herein.For example, a cardiac monitor or a cardiac stimulator may beimplemented to include one or more of the advantageous features orprocesses described below. It is intended that such a monitor,stimulator, or other implantable or partially implantable device neednot include all of the features described herein, but may be implementedto include selected features that provide for unique structures orfunctionality. Such a device may be implemented to provide a variety oftherapeutic or diagnostic functions.

FIG. 1 is an illustration of an example of portions of a system 100 thatincludes an IMD 105. Examples of IMB 105 include, without limitation, apacemaker, a cardioverter, a defibrillator, and other cardiac monitoringand therapy delivery devices, including cardiac devices that include orwork in coordination with one or more neuro-stimulating devices, drugs,drug delivery systems, or other therapies. In an example, the system 100shown is used to treat a cardiac arrhythmia. The IMD 105 typicallyincludes an electronics unit coupled by one or more cardiac leads 115 toa heart of a patient or subject. The electronics unit of the IMB 105typically includes components that are enclosed in a hermetically-sealedhousing sometimes referred to as a canister or “can.” The system 100also typically includes an IMB programmer or other external system 190that communicates one or more wireless signals 185 with the IMD 105,such as by using radio frequency (RF) or by one or more other telemetrymethods.

The example shown includes a right ventricular (RV) lead 115 having aproximal end and a distal end. The proximal end is coupled to a headerconnector 107. The distal end is configured for placement in the RV. TheRV lead 115 can include one or more of a proximal defibrillationelectrode 116, a distal defibrillation electrode 118 (e.g., RV Coil), anRV tip electrode 120A, and an RV ring electrode 120B. The defibrillationelectrode 116 is generally incorporated into the lead body such as in alocation suitable for supraventricular placement in the superior venacava (e.g., SVC Coil). In some examples, the RV lead 115 includes a ringelectrode 132 (e.g., SVC ring) in the vicinity of the proximaldefibrillation electrode 116. The defibrillation electrode 118 isincorporated into the lead body near the distal end, such as forplacement in the RV. The RV electrodes 120A and 120B can form a bipolarelectrode pair and are generally incorporated into the lead body at thelead distal end. The electrodes 116, 118, 120A, and 120B are eachelectrically coupled to IMD 105, such as through one or more conductorsextending within the lead body. The proximal defibrillation electrode116, distal defibrillation electrode 118, or an electrode formed on thecan of IMD 105 allow for delivery of cardioversion or defibrillationpulses to the heart.

The RV tip electrode 120A, RV ring electrode 120B, or an electrodeformed on the can of IMB 105 allow for sensing an RV electrogram signalrepresentative of RV depolarizations and delivering RV pacing pulses. Insome examples, the IMD includes a sense amplifier circuit to provideamplification or filtering of the sensed signal. Sensing and pacingallows the IMB 105 to adjust timing of the heart chamber contractions.

Some IMDs, such as shown in FIG. 1, may not include an electrode forsensing electrical activity in an atrium. For example, the IMB 105 canbe an ICD with single ventricular chamber sensing. The ICD can includean electrode attached to a single ventricular lead, and use intrinsiccardiac signals sensed with the ventricular electrode for arrhythmiadetection and discrimination (e.g., by rate sensing and/ordepolarization signal morphology analysis). The absence of sensingintrinsic atrial depolarizations (P-waves) may make arrhythmia detectionperform less well than a dual chamber ICD (e.g., an ICD including a leadfor placement in an atrium and a lead for placement in a ventricle).

Lack of atrial sensing makes it difficult for a clinician toretrospectively diagnose atrial tachyarrhythmia such as atrialfibrillation (AF) and atrial tachycardia (AT). Yet, AF/AT detection hasimportant diagnostic value. The time that a patient spends in AF issometimes called an AF burden. A device estimate of the AF burden isuseful to a clinician to determine which anti-arrhythmic therapy ortherapies to use, or which anticoagulant therapy or therapies toprescribe. Detection of AF is also useful for discriminating between AFand VT. And, as set forth above, occurrences of AT or AF with a fastventricular response is a major cause of inappropriate shocks.

FIG. 2 is a flow diagram of an example of a method 200 of detecting andclassifying atrial tachyarrhythmia using an IMB that does not havededicated atrial sensing circuits.

At block 205, an episode of tachyarrhythmia is detected using a devicesuch as an IMB. The tachyarrhythmia is detected from a cardiacdepolarization signal sensed from a ventricle using a dedicatedimplantable ventricular sensing circuit and in an absence of a dedicatedatrial chamber sensing circuit. For instance, the depolarization signalmay be sensed using bipolar electrodes 120A and 120B and a senseamplifier as discussed above in regard to FIG. 1, or the depolarizationsignal may be sensed as part of a wireless ECG which uses electrodesformed on the IMB housing. In certain examples, the device sensescardiac depolarization signals and detects tachyarrhythmia by detectinga depolarization rate that exceeds a tachyarrhythmia detection ratethreshold.

At block 210, a measure of stability of ventricular depolarization (V−V)intervals is determined using the depolarization signal. In certainexamples, the V−V intervals are measured by detecting R-waves in thedepolarization signal and measuring the intervals between R-waves (i.e.,RR intervals). R-waves of the QRS wave complex are indicative ofdepolarization of the ventricles.

The measure of stability indicates the variability of V−V intervaldifferences. In some examples of a stability measurement, pair-wisedifferences of V−V intervals are calculated (ΔV−V). When atachyarrhythmia episode is detected, the stability measurement isinitialized using an average of a specified number (e.g., four) V−Vinterval differences. The stability is then calculated on the fly duringthe episode. In certain examples, when a new V−V interval is detected, acurrent difference in the V−V interval is calculated and the stabilitymeasurement is calculated as the current difference minus the average ofthe previous differences.

In certain examples, a weighted stability calculation is used to assessstability. The stability measurement (S) is a weighted sum of theprevious stability measurement and the current stability measurement. Asan illustrative example, if weights of ⅞ and ⅛ are used, then

(S)_(CURRENT)=⅞*(S)_(PREVIOUS)+⅛*(ΔV-V).  (1)

If the V−V intervals are stable then the V−V intervals are uniform andthe differences will approach zero. If the V−V intervals are unstable,then the calculated differences will be greater than zero. The V−Vintervals are declared to be unstable if the weighted stabilitycalculation exceeds a predetermined threshold value.

Examples of methods and systems to detect arrhythmia and assess thestability of the rhythms are found in Gilkerson et al., U.S. Pat. No.6,493,579, entitled “System and Method for Detection EnhancementProgramming,” filed Aug. 20, 1999, which is incorporated herein byreference in its entirety.

For an atrial tachyarrhythmia such as AF, the V−V intervals will beirregular. Therefore, an atrial tachyarrhythmia is detectable withoutdedicated atrial sensing circuits by analysis of the V−V intervals.However, tachyarrhythmia discrimination is complicated by the fact thatV−V interval instability is not specific to atrial tachyarrhythmia. VTcan be irregular as well (e.g., at slower depolarization rates). Also,anti-arrhythmic drugs may cause monomorphic VT (MVT) to become markedlyirregular. Thus, VT may be misclassified as atrial tachyarrhythmia (andvice versa) in some circumstances.

A better approach is to monitor a rate of change of V−V intervalstability and use the rate of change in discrimination between differentforms of tachyarrhythmia. At block 215, a rate of change of the measureof stability is determined. In some examples, the rate of change ofstability (dS/dt) is calculated as approximately equal to

|S _(n) −S _(n-k) |/k,  (3)

where n and k are numbers of V−V intervals and k<n.

The rate of change indicates how the stability varies during thedetected tachyarrhythmia. For atrial tachyarrhythmia such as AF/AT, theonset of the tachyarrhythmia usually occurs with a sudden change in theV−V stability calculation. Because the stability calculation tends to benear zero for a stable rhythm, the value of the stability calculationwill exhibit a sudden increase for AF/AT. For many VTs, the V−Vstability calculation gradually changes to a value that indicatesinstability. Thus, a measure of the change in S with time (or a changeover k intervals) is a way to differentiate between AF/AT and VT.

At block 220, the detected tachyarrhythmia is classified as atrialtachyarrhythmia or ventricular tachyarrhythmia using the determined rateof change. At block 225, the tachyarrhythmia classification is providedto a user or process.

FIG. 3 is a block diagram 300 of portions of an example of an IMD 300 todetect and classify atrial tachyarrhythmia. The IMD 300 includes animplantable cardiac signal sensing circuit 305 designed for sensingelectrical depolarization signals in a ventricle, such as when thecoupled to an electrode shaped and sized to be placed in or near aventricle of a subject. It is to be noted that the IMD does not includededicated atrial sensing circuits.

The IMB 300 also includes a processor 307 communicatively coupled to thecardiac signal sensing circuit 305. The processor 307 may be a digitalsignal processor, ASIC, microprocessor, or other type of processor.Functions and algorithms performed by the processor correspond tomodules, which are software, hardware, firmware or any combinationthereof. Multiple functions may be performed in one or more modules asdesired, and the embodiments described are merely examples. Thecommunicative coupling allows the cardiac signal sensing circuit 305 andthe processor 307 to communicate even though there may be interveningcircuits between them. For example, the cardiac signal sensing circuit305 converts sensed cardiac depolarizations into electrical signals andthe electrical signals may be quantified for the processor using analogto digital (A/D) converters.

The processor 307 includes a signal analyzer module 310 configured todetermine a measure of stability of V−V intervals using thedepolarization signal. In some examples, the signal analyzer module 310determines a weighted stability calculation. The signal analyzer module310 also determines a rate of change of the measure of stability.

The processor 307 further includes a tachyarrhythmia discriminationmodule 315 to detect an episode of tachyarrhythmia using thedepolarization signal, such as when detecting a depolarization rate thatexceeds a tachyarrhythmia detection rate threshold for example. Thetachyarrhythmia discrimination module 315 then determines whether thedetected tachyarrhythmia is indicative of atrial tachyarrhythmia usingthe determined rate of change of stability, and provides thedetermination to a user or process. In some examples, the classificationmay be used by the IMB 300 to begin an anti-tachyarrhythmia treatmentsuch as anti-tachycardia pacing (ATP) or delivery of ananti-tachyarrhythmia drug. In some examples, the classification iscommunicated to an external device, such as an IMB programmer oradvanced patient management (APM) system.

In some examples, the tachyarrhythmia discrimination module 315classifies the detected tachyarrhythmia as atrial tachyarrhythmia whenthe rate of change of the measure of stability exceeds an atrialtachyarrhythmia rate of change detection threshold. In some examples,the tachyarrhythmia discrimination module 315 is configured to classifythe detected tachyarrhythmia as ventricular tachyarrhythmia when therate of change of the measure of stability is greater than a ventriculartachyarrhythmia rate of change detection threshold and is less than theatrial tachyarrhythmia rate of change detection threshold. This reflectsthe sudden change in stability evident during an onset of atrialtachyarrhythmia versus the gradual change in stability evident during anonset of ventricular tachyarrhythmia.

According to some examples, the tachyarrhythmia discrimination module315 may use the measure of V−V stability (S) or the rate of change ofthe measure of stability (dS/dt) to classify the tachyarrhythmia,depending on the detected depolarization rate. Classifying atrialtachyarrhythmia using S may be more reliable at tachyarrhythmia of lowerrates while using dS/dt may be more reliable at higher rates.

Thus in some examples, the tachyarrhythmia discrimination module 315classifies the detected tachyarrhythmia according to the rate of changeof the measure of stability when the ventricular rate or intervalsatisfies the specified threshold value (e.g., >170 beats per minute(bpm)), and classifies the detected tachyarrhythmia according to themeasure of stability otherwise (e.g., <170 bpm). The signal analyzermodule 310 determines a rate of change of the measure of stability whena ventricular depolarization rate or interval satisfies a specifiedthreshold rate or threshold interval value (e.g., a rate >170 bpm, or aV−V interval <350 ms).

In certain examples, the actual depolarization rate threshold used asthe cutoff between the use of S or dS/dt may be made programmable in thedevice and selected by a clinician. In certain examples, the thresholdis an absolute threshold set internally in the IMD and is notprogrammable. In certain examples, the threshold is dynamic and is apercentage of a running V−V interval average. In certain examples, thethreshold is characterized for each individual patient.

In some examples, once the tachyarrhythmia is classified, the IMD 300gathers statistics about the tachyarrhythmia. In certain examples, theIMD 300 includes a memory 320 and a communication circuit 330communicatively coupled to the tachyarrhythmia discrimination module315. The communication circuit 330 communicates information wirelesslywith a second separate device. The tachyarrhythmia discrimination module315 initiates storage of a segment of the depolarization signal uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia andwhen a duration of the detected tachyarrhythmia exceeds a durationthreshold. The tachyarrhythmia discrimination module 315 also initiatesstorage of a histogram of V−V depolarization intervals. Thetachyarrhythmia discrimination module 315 communicates the storedsegment and histogram to a second device at a later time. In certainexamples, the histogram indicates regular and irregular V−Vdepolarization intervals in the histogram data.

The IMD 300 may gather other statistics as well, such as a duration ofthe atrial tachyarrhythmia for example, which may also be communicatedto a second device. In certain examples, the second device is part of anadvanced patient management (APM) system and is able to communicatewirelessly with the IMD as well as communicate with other devices over acomputer network such as the internet or a cellular phone network. Incertain examples, a clinician can choose (e.g., by programming) atrigger condition of the statistics that causes the APM system to sendout an alert, such as when the duration exceeds a predeterminedthreshold duration for example.

In some examples, the second device may include a display or may relaythe histogram to a third device having a display. The histogram data maybe displayed with an indication (e.g., a color code) so the cliniciancan clearly see the difference in ventricular response when the patientis in atrial tachyarrhythmia. In certain examples, the histogram data issorted into an AF histogram or an AT histogram. In certain examples, thehistogram includes a rate histogram as well as trending of theventricular rate stability.

According to some examples, once a tachyarrhythmia has been classified,the tachyarrhythmia discrimination module 315 confirms theclassification with further analysis.

In certain examples, the IMD 300 uses a signal morphology analysis toconfirm the tachyarrhythmia classification. The memory 320 stores adepolarization signal morphology template 325. In certain examples, thesignal morphology template is stored in the memory 320 as a datastructure. The IMB 300 also includes a far-field sensing channel 335that provides a sensed far-field atrial and ventricular signal using anelectrode location that is outside of an atrium or ventricle. The sensedfar-field signal is a more global representation of activity in theatria and ventricles than a near-field signal or signals. In someexamples, the far-field sensing channel includes a unipolar sensingvector.

Returning to FIG. 1, in some examples, the unipolar sensing vectorincludes the coil electrode 116 configured to be placed in or near anSVC and an electrode incorporated into the housing or the header of theIMD 105. In some examples, the unipolar sensing vector includes thedistal defibrillation electrode 118 and an electrode incorporated intothe housing or the header of the IMD 105. In some examples, the unipolarsensing vector includes a ring electrode 132 configured to be placed inor near the SVC and the electrode incorporated into the housing or theheader of the IMB 105. In some examples, the far-field sensing channel335 is a far-field atrial sensing channel and includes the SVC coilelectrode 116 and the SVC ring electrode 132.

The tachyarrhythmia discrimination module 315 initiates sensing of thefar-field signal upon determining that the detected tachyarrhythmia isatrial tachyarrhythmia. The tachyarrhythmia discrimination module 315then initiates a comparison of a morphology of the sensed far-fieldsignal to the stored morphology template 325 by the signal analyzermodule 310. The tachyarrhythmia discrimination module 315 confirms theclassification as atrial tachyarrhythmia using the morphologycomparison.

In some examples, the stored morphology template 325 is associated withatrial tachyarrhythmia. The signal analyzer module 310 calculates ameasure of similarity between a segment of the sensed far-field signaland the morphology template 325. If the measure of similarity exceeds athreshold value, the tachyarrhythmia discrimination module 315 deems thedetected tachyarrhythmia to be atrial tachyarrhythmia.

In some examples, the stored morphology template 325 is associated withnormal sinus rhythm (NSR). The signal analyzer module 310 calculates ameasure of similarity between a segment of the sensed far-field signaland the morphology template, and calculates a central tendency of themeasure of similarity and a variance of the measure of similarity. Thetachyarrhythmia discrimination circuit is confirms the classification asatrial tachyarrhythmia when the central tendency of the measure ofsimilarity is above a central tendency threshold and the variance of themeasure of similarity is within a predetermined variance range.

In some examples, at least a portion of the signal processing isperformed by a second device. This offloads the processing demand of thesignal analyses from the IMD 300 to another device. Upon classifying thedetected tachyarrhythmia as atrial tachyarrhythmia and when a durationof the detected arrhythmia exceeds a duration threshold, thetachyarrhythmia discrimination module 315 again initiates storage of asegment of the sensed far-field signal. Instead of the IMD 300performing the additional analysis to confirm the classification of thedetected tachyarrhythmia, information is communicated to second devicefor the analysis.

For instance, if the additional analysis is morphology comparison, thestored segment is communicated to second device for comparison of afar-field signal morphology to a morphology template stored at thesecond device. The IMD 300 receives an indication whether the detectedtachyarrhythmia is atrial tachyarrhythmia from the second device via thecommunication circuit 330. If the indication is a confirmation of atrialtachyarrhythmia, the classification may be used by the IMD 300 to beginan anti-tachyarrhythmia treatment or the IMB 300 may begin gathering thepreviously described statistics.

According to some examples, V−V pattern recognition is used to detectatrial tachyarrhythmia in the absence of dedicated atrial sensingcircuitry. Alternating patterns of long and short V−V intervals can berecognized as being indicative of atrial tachyarrhythmia.

FIG. 4 is a flow diagram of an example of a method 400 of detectingatrial tachyarrhythmia using an IMB that does not have dedicated atrialsensing circuits. At block 405, an episode of tachyarrhythmia isdetected using a device such as an IMB. The tachyarrhythmia is detectedfrom a cardiac depolarization signal sensed from a ventricle using adedicated implantable ventricular sensing circuit and in an absence of adedicated atrial chamber sensing circuit. For example, thedepolarization signal may be sensed using bipolar electrodes 120A and120B and a sense amplifier as discussed above in regard to FIG. 1. Incertain examples, the device senses cardiac depolarization signals anddetects tachyarrhythmia by detecting a depolarization rate that exceedsa tachyarrhythmia detection rate threshold.

At block 410, a sudden presence of long and short V−V depolarizationintervals is detected using the depolarization signal. The suddenpresence of a characteristic pattern of short V−V intervals mixed withlonger intervals may be an indication of an atrial tachyarrhythmia eventsuch as AF. For example, the V−V intervals can have a pattern of“short-long-short-long, etc.” This pattern can be used to identify AF,without dedicated atrial sensing.

FIG. 5 shows an example of a “short-long” pattern of the V−V intervalsduring an AF episode. The top trace 505 shows what a bipolar atrialelectrogram sensed from the atrial lead would look like (if it werepresent) and the bottom trace 510 is a bipolar ventricular electrogramsensed from a ventricular lead (e.g., sensed with bipolar electrodes120A and 120B on lead 115 in FIG. 1, these electrodes are sometimesreferred to as a Vrate channel). The x-axis shows the data sampleindices (using a sampling rate of 200 Hz). The crosses on theventricular electrogram mark the ventricular events detected in theVrate channel.

In some examples, an interval is a long interval if it is longer than aspecified interval threshold, and an interval is a short interval if itis less than a specified interval threshold. One threshold may be usedto identify long and short threshold. In FIG. 5, the V−V intervals inthe data segment were (in milliseconds): 250, 347.5, 260, 350, 262.5,350, 260, 345, 255, 340, . . . . With a single threshold setting at, forexample, 300 ms, the “short-long” pattern can be determined. In certainexamples, a separate threshold is used to identify short thresholds andto identify long thresholds.

In some examples, a running average V−V interval is calculated. Aninterval is long if it exceeds the average V−V interval by apredetermined percentage, and an interval is short if it is less thanthe average V−V interval by a predetermined percentage. The shortintervals mixed with long intervals is deemed to be sudden if athreshold number of mixed short and long intervals occur within apredetermined interval of time or within a specified number of V−Vintervals.

At block 415, the detected tachyarrhythmia is classified as atrialtachyarrhythmia or ventricular tachyarrhythmia using a detected patternof long and short V−V depolarization intervals. Using the example ofFIG. 5, a captured repeated pattern of “short, long, short, long, . . .” may indicate AF. Thus, the detected tachyarrhythmia is classifiedaccording to a characteristic interval pattern recognized by the IMD.Other characteristic patterns may also be useful. At block 420, thetachyarrhythmia classification is provided to a user or process.

Returning to FIG. 3, to implement the method 400 the signal analyzermodule 310 measures V−V intervals. The tachyarrhythmia discriminationmodule 315 detects an episode of tachyarrhythmia using the senseddepolarization signal using any of the methods described previously. Thetachyarrhythmia discrimination module 315 detects a sudden presence oflong and short V−V depolarization intervals and classifies the detectedtachyarrhythmia as atrial tachyarrhythmia or ventricular tachyarrhythmiausing a detected pattern of long and short V−V depolarization intervals.The specific pattern of long and short intervals may be a defaultpattern or may be programmed into the device by a clinician specificallyfor the subject. The tachyarrhythmia discrimination module 315 thenprovides the tachyarrhythmia classification to a user or process.

Once the detected tachyarrhythmia has been classified, in some examplesthe tachyarrhythmia discrimination module 315 uses further analysis toconfirm the tachyarrhythmia. In certain examples, the tachyarrhythmia isconfirmed by a morphology analysis using a sensed far-field signal asdescribed herein.

In some examples, once the tachyarrhythmia is classified, the IMD 300gathers statistics about the tachyarrhythmia. In certain examples, thetachyarrhythmia discrimination module 315 initiates storage of a segmentof the sensed depolarization signal and initiates storage of a histogramof V−V depolarization intervals. The signal segment and the histogramare communicated to a second device.

As set forth previously, lack of atrial sensing makes it difficult for aclinician to retrospectively diagnose atrial tachyarrhythmia such as AFand AT, yet this information is often important to a physician orclinician. The several examples described herein provide for an IMD toautomatically diagnose atrial tachyarrhythmia even though dedicatedatrial chamber sensing circuit is absent in the device.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code can form portions of computerprogram products. Further, the code can be tangibly stored on one ormore volatile or non-volatile computer-readable media during executionor at other times. These computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAM's), read onlymemories (ROM's), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. (canceled)
 2. An apparatus comprising: an implantable cardiac signalsensing circuit, configured to provide a sensed depolarization signalfrom a ventricle; a processor communicatively coupled to the cardiacsignal sensing circuit, the processor including: a signal analyzermodule configured to measure V−V depolarization intervals; and atachyarrhythmia discrimination module configured to: detect an episodeof tachyarrhythmia using the measured V−V depolarization intervals;detect a sudden presence of long and short V−V depolarization intervals;classify the detected tachyarrhythmia as atrial tachyarrhythmia orventricular tachyarrhythmia using a detected pattern of long and shortV−V depolarization intervals; and provide the tachyarrhythmiaclassification to a user or process.
 3. The apparatus of claim 2,including: a memory communicatively coupled to the processor andconfigured to a store a signal morphology template; and a far-fieldsensing channel configured to provide a far-field atrial and ventricularsignal using an electrode location that is outside of an atrium orventricle, and wherein the tachyarrhythmia discrimination module isconfigured to: upon classifying the detected tachyarrhythmia as atrialtachyarrhythmia, initiate sensing of the far-field signal; and initiatea comparison a morphology of the far-field signal to a stored morphologytemplate by the signal analyzer module; and confirm the classificationas atrial tachyarrhythmia using the morphology comparison.
 4. Theapparatus of claim 3, wherein the signal analyzer module is configuredto: calculate a measure of similarity between a segment of the far-fieldsignal and the morphology template, wherein the stored morphologytemplate is representative of normal sinus rhythm; calculate a centraltendency of the measure of similarity and a variance of the measure ofsimilarity, and wherein the tachyarrhythmia discrimination module isconfigured to confirm the classification as atrial tachyarrhythmia whenthe central tendency of the measure of similarity is above a centraltendency threshold, the variance of the measure of similarity is withina variance range, and the depolarization rate or interval satisfies arate or interval detection threshold.
 5. The apparatus of claim 2,including: a memory communicatively coupled to the processor; and acommunication circuit, communicatively coupled to the processor,configured to communicate information wirelessly with a second separatedevice, and wherein the tachyarrhythmia discrimination module isconfigured to: upon classifying the detected tachyarrhythmia as atrialtachyarrhythmia, initiate storage of a segment of the depolarizationsignal when a duration of the detected arrhythmia exceeds a durationthreshold; initiate storage of a histogram of V−V depolarizationintervals, wherein the histogram indicates regular and irregular V−Vdepolarization intervals; and communicate the stored segment andhistogram from an implantable medical device to a second device.
 6. Amethod comprising: detecting an episode of tachyarrhythmia using adepolarization signal sensed from a ventricle in an absence of adedicated atrial chamber sensing circuit; detecting a sudden presence oflong and short V−V depolarization intervals using the depolarizationsignal; classifying the detected tachyarrhythmia as atrialtachyarrhythmia or ventricular tachyarrhythmia using a detected patternof long and short V−V depolarization intervals; and providing thetachyarrhythmia classification to a user or process.
 7. The method ofclaim 6, including: upon classifying the detected tachyarrhythmia asatrial tachyarrhythmia, sensing a second signal using a far-fieldsensing channel; and comparing a morphology of the second sensed signalto a morphology template, and wherein classifying the tachyarrhythmiaincludes confirming the classification as atrial tachyarrhythmia usingthe morphology comparison.
 8. The method of claim 6, including uponclassifying the detected tachyarrhythmia as atrial tachyarrhythmia,storing a segment of the depolarization signal when a duration of thedetected arrhythmia exceeds a duration threshold; storing a histogram ofV−V depolarization intervals, wherein the histogram indicates regularand irregular V−V depolarization intervals; and communicating the storedsegment and histogram from an implantable medical device to a seconddevice.